1. Technical Field
The present invention relates in general to rifles and more particularly to apparatus for adapting a rifle to fire a projectile of different design than the rifle was manufactured to fire.
2. Background Information
Presently, the basic United States Army infantry rifle is the M-16 and the cartridge designed to be fired from this rifle is the M-193. At the time of the present invention, NATO, through its various technical panels and study commissions, was conducting a technical evaluation program to determine the best cartridge to be used in connection with its new Infantry Rifle Standardization Agreement. Among the candidates for selection was the Belgium SS-109 cartridge. Certain logistical and technical problems would have arised for the United States infantry if the SS-109 projectile had been selected as the desirable cartridge for the standardization effort. Although the Belgium SS-109 and the U.S. M-193 share basically the same physical envelope, the projectile designs are sufficiently different that the SS-109 requires a higher spin rate to achieve gyroscopic stability than the M-193. If the Belgium SS-109 is fired from the standard U.S. M-16 rifle, problems of reduced effectiveness at normal firing temperatures and total instability at reduced air temperatures occur, thus compromising the rifle's usefulness.
Should the Belgium SS-109 cartridge have been chosen for the NATO infantry standardization effort then prompt cooperation by the United States Government would have meant replacing all existing M-16 rifles with barrels having rifling characteristics like those of a Belgian rifle designed to fire the SS-109 cartridge, or designing an adaptor which could be field installed to provide the additional spin rate needed to stablize the SS-109 projectile fired from the U.S. M-16. The present is the result of extensive research involving this latter option.
Previous attempts to design a similar adaptor for attachment to the end of a rifle have generally failed. These attempts have been unsuccessful in maintaining gyroscopic stability of the projectile upon its exit from the adaptor, primarily because of continued projectile angular acceleration after the projectile has exited from the adaptor, an inherent result of the approach taken by these prior attempts. Projectile angular acceleration after the projectile has exited from the adaptor will cause the projectile to yaw or oscillate, thus reducing the overall effectiveness of the weapon. This projectile angular acceleration results from the prior art use of an exponential function to progressively change the rifle twist rate.
Therefore, there exists a genuine need for an effective, inexpensive adaptor for attachment to the end of a rifle which will allow an individual to fire from the rifle a projectile, different than the projectile originally designed for the rifle, without substantial degradation in the overall accuracy and throw distance of the rifle.